Adipic acid

Names
Preferred IUPAC name

Hexanedioic acid

Other names

Adipic acid
Butane-1,4-dicarboxylic acid
Hexane-1,6-dioic acid
1,4-butanedicarboxylic acid

Identifiers

CAS Number

* 124-04-9 Y

3D model (JSmol)

* Interactive image
* Interactive image

Beilstein Reference

| 1209788
ChEBI |

* CHEBI:30832 Y

ChEMBL |

* ChEMBL1157 Y

ChemSpider |

* 191 Y

ECHA InfoCard | 100.004.250
EC Number |

* 204-673-3

E number | E355 (antioxidants, ...)

Gmelin Reference

| 3166
KEGG |

* D08839 Y

PubChem CID

* 196

RTECS number |

* AU8400000

UNII |

* 76A0JE0FKJ Y

UN number | 3077

CompTox Dashboard (EPA)

* DTXSID7021605

InChI

* InChI=1S/C6H10O4/c7-5(8)3-1-2-4-6(9)10/h1-4H2,(H,7,8)(H,9,10) Y

Key: WNLRTRBMVRJNCN-UHFFFAOYSA-N Y

* InChI=1/C6H10O4/c7-5(8)3-1-2-4-6(9)10/h1-4H2,(H,7,8)(H,9,10)

Key: WNLRTRBMVRJNCN-UHFFFAOYAY

SMILES

* O=C(O)CCCCC(=O)O

* C(CCC(=O)O)CC(=O)O

Properties

Chemical formula

| C6H10O4
Molar mass | 146.142 g·mol−1
Appearance  | White crystals[1]
Monoclinic prisms[2]
Odor | Odorless
Density | 1.360 g/cm3
Melting point | 152.1 °C (305.8 °F; 425.2 K)
Boiling point | 337.5 °C (639.5 °F; 610.6 K)

Solubility in water

| 14 g/L (10 °C)
24 g/L (25 °C)
1600 g/L (100 °C)
Solubility | Very soluble in methanol, ethanol
soluble in acetone, acetic acid
slightly soluble in cyclohexane
negligible in benzene, petroleum ether
log P | 0.08
Vapor pressure | 0.097 hPa (18.5 °C) = 0.073 mmHg
Acidity (pKa)  | 4.43, 5.41
Conjugate base | Adipate
Viscosity | 4.54 cP (160 °C)
Structure

Crystal structure

| Monoclinic
Thermochemistry

Std enthalpy of
formation (ΔfH⦵298)

| −994.3 kJ/mol[3]
Hazards
GHS labelling:

Pictograms

Signal word

| Warning

Hazard statements

| H319

Precautionary statements

| P264, P280, P305+P351+P338, P337+P313
NFPA 704 (fire diamond)  |

Flash point | 196 °C (385 °F; 469 K)

Autoignition
temperature

| 422 °C (792 °F; 695 K)
Lethal dose or concentration (LD, LC):

LD50 (median dose)

| 3600 mg/kg (rat)
Safety data sheet (SDS)  | External MSDS
Related compounds

Related dicarboxylic acids

| glutaric acid
pimelic acid

Related compounds

| hexanoic acid
adipic acid dihydrazide
hexanedioyl dichloride
hexanedinitrile
hexanediamide

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Infobox references

Chemical compound

Adipic acid or hexanedioic acid is the organic compound with the formula (CH2)4(COOH)2. From an industrial perspective, it is the most important dicarboxylic acid: about 2.5 billion kilograms of this white crystalline powder are produced annually, mainly as a precursor for the production of nylon. Adipic acid otherwise rarely occurs in nature,[4] but it is known as manufactured E number food additive E355. Salts and esters of adipic acid are known as adipates.

## Preparation and reactivity

[edit]

Adipic acid is produced by oxidation of a mixture of cyclohexanone and cyclohexanol, which is called KA oil, an abbreviation of ketone-alcohol oil. Nitric acid is the oxidant. The pathway is multistep. Early in the reaction, the cyclohexanol is converted to the ketone, releasing nitrous acid:

HOCH(CH2)5 \+ HNO3 → O=C(CH2)5 \+ HNO2 \+ H2O

The cyclohexanone is then nitrosated, setting the stage for the scission of the C-C bond:

HNO2 \+ HNO3 → [NO+]NO3]− \+ H2O
O=C(CH2)5 \+ NO+ → O=C(CHNO)(CH2)4 \+ H+

Side products of the method include glutaric and succinic acids. Nitrous oxide is produced in about one to one mole ratio to the adipic acid,[5] as well, via the intermediacy of a nitrolic acid.[4]

Related processes start from cyclohexanol, which is obtained from the hydrogenation of phenol.[4][6]

### Alternative methods of production

[edit]

Several methods have been developed by carbonylation of butadiene. For example, the hydrocarboxylation proceeds as follows:[4]

CH2=CH−CH=CH2 \+ 2 CO + 2 H2O → HO2C(CH2)4CO2H

Another method is oxidative cleavage of cyclohexene using hydrogen peroxide.[7] The waste product is water.

Historically, adipic acid was prepared by oxidation of various fats,[8] thus the name (ultimately from Latin adeps, adipis – "animal fat"; cf. adipose tissue).

### Reactions

[edit]

Adipic acid is a dibasic acid (it has two acidic groups). The pKa values for their successive deprotonations are 4.41 and 5.41.[9]

With the carboxylate groups separated by four methylene groups, adipic acid is suited for intramolecular condensation reactions. Upon treatment with barium hydroxide at elevated temperatures, it undergoes ketonization to give cyclopentanone.[10]

## Uses

[edit]

About 60% of the 2.5 billion kg of adipic acid produced annually is used as monomer for the production of nylon[11] by a polycondensation reaction with hexamethylene diamine forming nylon 66. Other major applications also involve polymers; it is a monomer for production of polyurethane and its esters are plasticizers, especially in PVC.[12]

### In medicine

[edit]

Adipic acid has been incorporated into controlled-release formulation matrix tablets to obtain pH-independent release for both weakly basic and weakly acidic drugs. It has also been incorporated into the polymeric coating of hydrophilic monolithic systems to modulate the intragel pH, resulting in zero-order release of a hydrophilic drug. The disintegration at intestinal pH of the enteric polymer shellac has been reported to improve when adipic acid was used as a pore-forming agent without affecting release in the acidic media. Other controlled-release formulations have included adipic acid with the intention of obtaining a late-burst release profile.[13]

### In foods

[edit]

Small but significant amounts of adipic acid are used as a food ingredient as a flavorant and gelling aid.[14] It is used in some calcium carbonate antacids to make them tart. As an acidulant in baking powders, it avoids the undesirable hygroscopic properties of tartaric acid.[2] Adipic acid, rare in nature, does occur naturally in beets, but this is not an economical source for commerce compared to industrial synthesis.[15]

## Safety

[edit]

Adipic acid, like most carboxylic acids, is a mild skin irritant. It is mildly toxic, with a median lethal dose of 3600 mg/kg for oral ingestion by rats.[4]

## Environmental

[edit]

The production of adipic acid is linked to emissions of N
2O,[16] a potent greenhouse gas and cause of stratospheric ozone depletion. At adipic acid producers DuPont and Rhodia (now Invista and Solvay, respectively), processes have been implemented to catalytically convert the nitrous oxide to innocuous products:[17]

2 N2O → 2 N2 \+ O2

## Adipate salts and esters

[edit]

Structural formula of the adipate dianion

The anionic (HO2C(CH2)4CO2−) and dianionic (−O2C(CH2)4CO2−) forms of adipic acid are referred to as adipates. An adipate compound is a carboxylate salt or ester of the acid.

Some adipate salts are used as acidity regulators, including:

* Sodium adipate (E number E356)
* Potassium adipate (E357)

Some adipate esters are used as plasticizers, including:

* Bis(2-ethylhexyl) adipate
* Dioctyl adipate
* Dimethyl adipate

## References

[edit]

1. ^ Mac Gillavry, C. H. (2010). "The crystal structure of adipic acid". Recueil des Travaux Chimiques des Pays-Bas. 60 (8): 605–617. doi:10.1002/recl.19410600805.
2. ^ a b "Adipic Acid". The Merck Index. Royal Society of Chemistry. 2013. Retrieved 2 March 2017.
3. ^ Haynes, W. M., ed. (2013). CRC Handbook of Chemistry and Physics (94th ed.). Boca Raton, Florida: CRC Press. ISBN 978-1-4665-7114-3.
4. ^ a b c d e Musser, M. T. (2005). "Adipic Acid". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a01_269. ISBN 3527306730.
5. ^ Parmon, V. N.; Panov, G. I.; Uriarte, A.; Noskov, A. S. (2005). "Nitrous oxide in oxidation chemistry and catalysis application and production". Catalysis Today. 100 (2005): 115–131. doi:10.1016/j.cattod.2004.12.012.
6. ^ Ellis, B. A. (1925). "Adipic Acid". Organic Syntheses. 5: 9; Collected Volumes, vol. 1, p. 560.
7. ^ Sato, K.; Aoki, M.; Noyori, R. (1998). "A "Green" route to adipic acid: direct oxidation of cyclohexenes with 30 percent hydrogen peroxide". Science. 281 (5383): 1646–47. Bibcode:1998Sci...281.1646S. doi:10.1126/science.281.5383.1646. PMID 9733504.
8. ^ Ince, Walter (1895). "Preparation of adipic acid and some of its derivatives". Journal of the Chemical Society, Transactions. 67: 155–159. doi:10.1039/CT8956700155.
9. ^ Cornils, Boy; Lappe, Peter (2000). "Dicarboxylic Acids, Aliphatic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a08_523. ISBN 3527306730.
10. ^ Thorpe, J. F.; Kon, G. A. R. (1925). "Cyclopentanone". Organic Syntheses. 5: 37; Collected Volumes, vol. 1, p. 192.
11. ^ "Adipic Acid". Archived from the original on 2015-05-18. Retrieved 2015-05-09. PCI abstract for adipic acid
12. ^ "Polyvinylchloride - an overview | ScienceDirect Topics". www.sciencedirect.com. Retrieved 2023-11-10.
13. ^ Roew, Raymond (2009), "Adipic Acid", Handbook of Pharmaceutical Excipients, pp. 11–12
14. ^ "Cherry Jell-O Nutrition Facts". Kraft Foods. Archived from the original on 24 September 2019. Retrieved 21 Mar 2012.
15. ^ American Chemical Society (9 February 2015). "Molecule of the Week: Adipic Acid".
16. ^ US EPA (12 August 2013). "U.S. Greenhouse Gas Inventory Report, Chapter 4. Industrial Processes" (PDF). Retrieved 2013-11-29.
17. ^ Reimer, R. A.; Slaten, C. S.; Seapan, M.; Koch, T. A.; Triner, V. G. (2000). "Adipic Acid Industry — N2O Abatement". Non-CO2 Greenhouse Gases: Scientific Understanding, Control and Implementation. Netherlands: Springer. pp. 347–358. doi:10.1007/978-94-015-9343-4_56. ISBN 978-94-015-9343-4.

## Appendix

[edit]

* U.S. FDA citations – GRAS (21 CFR 184.1009), Indirect additive (21 CFR 175.300, 21 CFR 175.320, 21 CFR 176.170, 21 CFR 176.180, 21 CFR 177.1200, 21 CFR 177.1390, 21 CFR 177.1500, 21 CFR 177.1630, 21 CFR 177.1680, 21 CFR 177.2420, 21 CFR 177.2600)
* European Union Citations – Decision 1999/217/EC – Flavoing Substance; Directive 95/2/EC, Annex IV – Permitted Food Additive; 2002/72/EC, Annex A – Authorized monomer for Food Contact Plastics

## External links

[edit]

* International Chemical Safety Card 0369
* SIDS Initial Assessment Report for Adipic acid from the Organisation for Economic Co-operation and Development (OECD)
* adipic acid on chemicalland

* v
* t
* e

Linear saturated dicarboxylic acids (HO2C-R-CO2H)

* Ethanedioic acid (Oxalic acid) (CO2H)
* Propanedioic acid (Malonic acid) CH2(CO2H)
* Butanedioic acid (Succinic acid) C2H4(CO2H)
* Pentanedioic acid (Glutaric acid) C3H6(CO2H)
* Hexanedioic acid (Adipic acid) C4H8(CO2H)
* Heptanedioic acid (Pimelic acid) C7H12O4
* Octanedioic acid (Suberic acid) C8H14O4
* Nonanedioic acid (Azelaic acid) C9H16O4
* Decanedioic acid (Sebacic acid) C10H18O4
* Dodecanedioic acid C12H22O4
* Tredecanedioic acid (Brassylic acid) C13H24O4
* Hexadecanedioic acid (Thapsic acid) C16H30O4
* Docosanedioic acid (Phelogenic acid) C22H42O4

Category:Dicarboxylic acids

Authority control databases: National |

* Germany

|

*[CID]: Compound ID
*[EPA]: U.S. Environmental Protection Agency
*[H319]: H319: Causes serious eye irritation
*[P264]: P264: Wash ... thoroughly after handling.
*[P280]: P280: Wear protective gloves/protective clothing/eye protection/face protection.
*[P305+P351+P338]: P305+P351+P338: IF IN EYES: Rinse continuously with water for several minutes. Remove contact lenses if present and easy to do. Continue rinsing.
*[P337+P313]: P337+P313: If eye irritation persists: Get medical advice/attention.
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